A frequency synthesizing device, for example, a PLL synthesizer is generally used for the frequency synthesis in AM.multidot.SSB(U, L) transceivers. The synthesizer of this kind includes generally a single crystal oscillator or a plurality of crystal oscillators.
An AM.multidot.SSB(U, L) transceiver employing a PLL synthesizer including a single crystal oscillator is disclosed in, for example, U.S. Pat. No. 3,983,484. However, the transceiver disclosed in this U.S. patent has the following defects:
(a) For the synthesis of the transmitting and receiving frequencies of the AM.multidot.SSB(U, L) transceiver, exclusive SSB filters for the upper and lower side bands are indispensably required.
(b) Due to the fact that the output frequency of the PLL synthesizer during the signal transmission differs from that during the signal reception, it is necessary to change over the variable frequency division ratio N of the programmable divider depending on the transmission or reception, and the voltage controlled oscillator must be repeatedly locked and unlocked depending on the signal transmission or reception.
(c) For the purpose of signal transmission, fine adjustment is required to shift the fundamental frequency, 10.24 MHz of the PLL synthesizer to 10.238102 MHz. Therefore, there occurs a maximum frequency shift of 80 Hz in the carrier frequencies for the 1st to 40th channels, as follows:
1st channel (26.965 MHz) ##EQU1##
40th channel (27.405 MHz) ##EQU2##